Organocatalysts for the Reaction of Dimethyl Carbonate with 2,4-Diaminotoluene

Four nitrogen-containing organic compounds [1,5,7-triazabicyclo(4,4,0)dec-5-ene, 4-(N,N-dimethylamino)pyridine, N-methylimidazole, and l-proline] have been tested as organocatalysts for the reaction of dimethyl carbonate with an aromatic diamine, 2,4-diaminotoluene (DAT). Although, generally, N-methylation was the predominant process, variable proportions of N-carbamoylation were also observed. Reaction kinetics indicates that N-methylation and N-carbamoylation are independent and parallel processes. DAT conversion increases as the temperature increased over the range of 105−125 °C. Besides the nature of the organocatalyst, the ratio between N-methylation/N-carbamoylation was influenced by the DAT-to-DMC ratio: higher DAT proportions increased the DAT conversion and favored N-carbamoylation. 4-(N,N-dimethylamine)pyridine was determined to be the most active organocatalyst of the series and, under certain conditions, can lead to selective N-methylation with high conversion.